Apparatus for electrostatic separation



APPARATUS FOR ELECTROSTATIC SEPARATION Filed March l, 1935 G. GRAVE ETAL, I 2,072,50fi

Patented Mar. v2, 1937 2,072,501 v APPARATUS FOR nI g r nosrA'ricsErAnA- Georg Grave, FrankIort-on-the-Main-Heddernhelm, and Erich Oppen,Hanover, Germany, as-

signors to American Lurgi Corporation, New

York, N.-Y., a corporation oi New York Application March 1 1935, SerialNo. 8,966

In Germany January 16, 1935 3 Claims.

This invention relates to an apparatus for electrostatic separation.

In the case of electrostatic separators operating on the attractionprinciple the attraction of 5 the particles takes place as soon as theelectric force of attraction overcomes the other forces.

The invention will be explained with reference to the accompanyingdrawing in which Fig. 1 is a diagrammatic representation of the forcesinvolved. in an electrostatic separator in whichthe particles arecarried on one drum into an electrostatic field created by an adjacent.1. .1". and

Fig. 2 is a diagrammatic representation of the forces involved'inaccordance with the invention.

If there exists an electrostatic field between the feeder drum I and thehigh-tension drum 2 (Fig.

1) the lifting of the particle A takes place as soon as the chargeassumes such a value, that they sum of centrifugal force AB pluselectrostatic force of attraction BC becomes greater than the force ofgravity AD sin a. From the above itresuits that a good separation is notpossible between two drums; since, the longer the particle remains onthe revolving drum I, the more time is available to accumulate anelectrical charge, and the stronger the electrical attraction will be.This is the reason why generally electrostatic action between two drumsis only practicable 'if there are very great differences of weightbetween the particles which are to be separated.

- Fig. 2 shows a way to avoid these disadvantages and to enlarge thefield of usefulness for those cases where the difference between poweroff attraction and time necessary for charging the 5 particles is onlysmall. The material to be separated is fed through the channel 9 to themetallic drum I, which is grounded. The material to be treated isentirely shielded against the electrostatic field emanating from drum 2by means 40 of two metallic drums 3 and 4, which are grounded, and thesurfaces of sheet-iron or the like 5 and 6. Only the space between 3 and4 is influenced by the electric field. Now, it is possible to adjust thedrums 3 and 4 in such a manner 45 that only the particles which hardlytake an electric charge or the particles which are easier to beattracted are lifted from drum i and go to receptacle 8, whereas theparticles which are not attracted fall into receptacle 1. The path of 50the lines of force is represented in Fig. 2. The

material to be treated coming from the space, en-

(Cil. 209-129) tirelyfree from force lines, on the left of drum 3,enters very suddenly an almost homogeneous field so that the attractionoccurs equally suddenly.

Of course regulation may also be obtained by means of the revolvingvelocity of the drums. It is advantageous to run the drum 2 at such arate of speed as to avoid the tailing back of particles lifted by it onto drum i. It has been attempted heretofore to obtain shielding bysemi-conducting separating tongues. Leaving out of the question thatthis means of shielding really shields only part of the lines of force,these tongues have thedisadvantage, that they get clogged with materialin continual service and the apparatus becomes incapable of functioning.This drawback is avoided by using revolving drums, which can be easilycleaned by means of scrapers. A further advantage of the inventionconsists in the fact that the device is protected against the chemicalinfluence of the ozone, which forms inevitably, since no semi-conductingparts are used which, as is already known, often lose conductivity underthe action of ozone.

We claim:--

1. Apparatus for electrostatic separation comprising a revolvinggrounded carrier drum, means for delivering the material to be separatedto said carrier drum, a relatively high potential revolving drum spacedfrom said carrier drum serving to create a high potential electrostaticfield between said drums, and two grounded revolving drums disposed atopposite sides of said field and serving to confine the electrostaticfield operative on the material to the space therebetween.

2. Apparatus for electrostatic separation comprising a groundedrevolving carrier drum, means for supplying material to be separated tosaid carrier drum, a revolving high potential drum spaced from saidcarrier drum and creating an electrostatic field through which thematerial on said carrier drum must pass, and means for shielding thematerial and confining said electrostatic field comprising groundedscreening drums situated on each side of the space between said carrierdrum and said high potential drum.

3. Apparatus for electrostatic separation as defined in claim 2 in whichsaid screening drums are adjustable.

GEORG GRAVE. ERICH OPPEN.

